Cu–Ni alloying effects When nickel is added to copper to form copper–nickel alloys, which combination of properties is generally improved compared with pure copper?

Introduction / Context:
Copper–nickel (Cu–Ni) alloys are widely used in marine condensers, coinage, and corrosion-resistant components. Alloy additions change both strength and formability, making them attractive where pure copper is too soft.

Given Data / Assumptions:

• Moderate nickel levels (e.g., 10–30%) are considered.
• Properties compared to annealed or worked pure copper.
• Service often demands both toughness and formability.

Concept / Approach:
Nickel in solid solution strengthens copper by hindering dislocation motion (solid-solution strengthening) while retaining good ductility. As a result, Cu–Ni alloys show higher yield and tensile strengths than copper with only modest reductions in elongation. They also provide improved corrosion resistance, especially in seawater.

Step-by-Step Solution:
Identify mechanism: solid-solution strengthening from Ni atoms in the Cu lattice.Evaluate property trend: increased strength with usable ductility enables forming and service load capacity.Compare options: “strength and ductility” best captures the balanced improvement.Therefore choose option (d).

Verification / Alternative check:
Property charts for 70–30 Cu–Ni show significantly higher strength than copper while elongation remains respectable (often 20–40% in annealed conditions).

Why Other Options Are Wrong:
Machinability is not the primary gain; hardness alone is incomplete; “hardness and strength” ignores maintained ductility; electrical conductivity decreases with Ni addition rather than improves.

Common Pitfalls:
Assuming strength increase always sacrifices ductility severely; for Cu–Ni, the trade-off is moderate and often acceptable.

Final Answer:
strength and ductility